MIC2583 Micrel Semiconductor, MIC2583 Datasheet - Page 14

• Manufacturer Part Number: MIC2583
• Description: Single Channel Hot Swap Controllers
• Manufacturer: Micrel Semiconductor

MIC2582/MIC2583
GATE Capacitance Dominated Start-Up
In this case, the value of the load capacitance relative to the
GATE capacitance is small enough such that the load current
during start-up never exceeds the current limit threshold as
determined by Equation 3. The minimum value of C
will ensure that the current limit is never exceeded is given by
the equation below:
where C
capacitance (C
connected to the GATE pin of the MIC2582/83 to ground. Once
C
the output slew rate for gate capacitance dominated start-up.
Table 1 depicts the output slew rate for various values of C
Current Limiting and Dual-Level Circuit Breaker
Many applications will require that the inrush and steady state
supply current be limited at a specific value in order to protect
critical components within the system. Connecting a sense
resistor between the VCC and SENSE pins sets the nominal
current limit value of the MIC2582/83 and the current limit is
calculated using Equation 2.
The MIC2582/83 also features a dual-level circuit breaker
triggered via 50mV and 100mV current limit thresholds sensed
across the VCC and SENSE pins. The first level of the circuit
breaker functions as follows. For the MIC2583/83R, once the
voltage sensed across these two pins exceeds 50mV, the
overcurrent timer, its duration set by capacitor C
to ramp the voltage at CFILTER using a 6.5 A constant current
source. If the voltage at CFILTER reaches the overcurrent timer
threshold (V
ground as the circuit breaker trips and the GATE output is
immediately shut down. The default overcurrent time period for
the MIC2582/83 is 5 s. For the second level, if the voltage
sensed across VCC and SENSE exceeds 100mV at any time,
the circuit breaker trips and the GATE shuts down immediately,
bypassing the overcurrent time period. To disable current limit
and circuit breaker operation, tie the SENSE and VCC pins
together and the CFILTER (MIC2583/83R) pin to ground.
Output Undervoltage Detection
The MIC2582/83 employ output undervoltage detection by
monitoring the output voltage through a resistive divider con-
nected at the FB pin. During turn on, while the voltage at the FB
pin is below the threshold (V
Once the FB pin voltage crosses V
MIC2582/MIC2583
GATE
Table 1. Output Slew Rate Selection for GATE
C
dV
is determined, use the following equation to determine
GATE
C
0.001 F
0.01 F
0.1 F
1 F
OUT
GATE
GATE
TH
Capacitance Dominated Start-Up
/dt
(min)
) of 1.24V, then CFILTER immediately returns to
ISS
is the summation of the MOSFET input
) and the value of the external capacitor
C
I
GATE
GATE
I
GATE
I
I
LIM
GATE
= 17 A
FB
C
), the /POR pin is asserted low.
LOAD
dV
17V/ms
1.7V/ms
0.17V/ms
0.017V/ms
FB
OUT
, a 2.5 A current source
/dt
FILTER
GATE
(5)
(6)
, starts
GATE
that
.
14
charges capacitor C
1.24V, the time period t
to ground and the /POR pin goes HIGH. If the voltage at FB
drops below V
least one timing cycle defined by t
Information for an example).
Power-On Reset and Overcurrent Timer Delays
The Power-On Reset delay, t
/POR pin to go HIGH once the voltage at the FB pin exceeds the
power-good threshold (V
sets the interval and is determined by using Equation 1 with V
substituted for V
where the Power-On Reset threshold (V
(I
For the MIC2583/83R, a capacitor connected to CFILTER is
used to set the timer which activates the circuit breaker during
overcurrent conditions. When the voltage across the sense
resistor exceeds the slow trip current limit threshold of 50mV,
the overcurrent timer begins to charge for a time period
(t
connected to CFILTER and for the MIC2582, t
to 5 s. If t
and the GATE output is immediately pulled to ground. For the
MIC2583/83R, the following equation is used to determine the
overcurrent timer period, t
where V
the overcurrent timer current, is 6.5 A. Tables 2 and 3 provide
a quick reference for several timer calculations using select
standard value capacitors.
Table 2. Selected Power-On Reset and Start-Up Delays
CPOR
OCSLOW
t
OCSLOW
0.033 F
0.01 F
0.02 F
0.05 F
0.33 F
0.47 F
0.1 F
C
t
1 F
Table 3. Selected Overcurrent Timer Delays
) are typically 1.24V and 2.5 A, respectively.
POR
POR
TH
), determined by C
OCSLOW
, the CFILTER timer threshold, is 1.24V and I
0.033 F
C
2200pF
4700pF
8200pF
0.22 F
0.47 F
680pF
0.1 F
C
FILTER
C
FB
FILTER
POR
START
for more than 10 s, the /POR pin resets for at
elapses, then the circuit breaker is activated
POR
I
CPOR
V
I
. The resulting equation becomes:
POR
TIMER
TH
V
. Once the CPOR pin voltage reaches
FB
TH
OCSLOW
t
120ms
1.2ms
2.4ms
12ms
40ms
56ms
START
). A capacitor connected to CPOR
4ms
6ms
elapses as the CPOR pin is pulled
0.5 C
FILTER
POR
0.19 C
.
, is the time period for the
POR
. When no capacitor is
POR
FILTER
TH
t
F
OCSLOW
) and timer current
(See Applications
420 s
900 s
130 s
1.5ms
19ms
42ms
90ms
6ms
OCSLOW
( F)
16.5ms
165ms
235ms
500ms
10ms
25ms
50ms
t
5ms
POR
(7)
April 2003
(8)
defaults
Micrel
TIMER
TH
,